1. Field of the Invention
The present invention relates to a technique for assisting endoscopic observation in an endoscopic surgery, an endoscopic examination and the like with an endoscope inserted into the body cavity of a subject to be examined. Especially, the present invention relates to a technique for assisting endoscopic observation by using a virtual endoscope image representing the body cavity of the subject to be examined.
2. Description of the Related Art
In recent years, endoscopic surgeries, such as a laparoscopic surgery and a thoracoscopic surgery, drew attention. The endoscopic surgeries do not require laparotomy, thoracotomy, and the like. The endoscopic surgeries require incision only to form two or three holes with diameters of approximately a few centimeters for introduction of an endoscope and a treatment tool. Therefore, the endoscopic surgeries have a merit that a burden on a patient is extremely low. However, a surgery in a narrow field of view of the endoscope is technically difficult, and an operation needs to be performed by a skilled doctor. If a blood vessel or an organ of a patient is damaged by mistake, and bleeding occurs, the endoscopic surgery must be switched to a conventional surgery including laparotomy, thoracotomy, or the like.
Meanwhile, a virtual endoscope technique for generating an image similar to an endoscopic image from three-dimensional volume data obtained by imaging by CT or the like is known. This technique is widely used in North America especially to detect a tumor in a large intestine only by imaging by CT without performing an endoscopic examination.
Further, a technique for assisting an endoscopic surgery by using a virtual endoscope image has been proposed.
For example, Japanese Unexamined Patent Publication No. 2002-263053 (Patent Document 1) discloses an apparatus for displaying a real endoscope image obtained by imaging by an endoscope and a virtual endoscope image in such a manner to be superimposed one on the other. In Patent Document 1, the position of the endoscope is detected by a sensor, and the detected position is used as a viewpoint to generate the virtual endoscope image having an angle of view wider than that of the endoscope.
Further, Japanese Unexamined Patent Publication No. 2005-021353 (Patent Document 2) discloses an apparatus for displaying a synthesis image and a real endoscope image. In Patent Document 2, the position of an endoscope is detected in real time, and a virtual endoscope image having the same field of view as that of the endoscope, and that visualizes an arrangement of blood vessels in the field of view is generated. Further, the position of a treatment tool used in an endoscopic surgery is detected in real time, and the synthesis image representing the treatment tool at the position of the treatment tool in the virtual endoscope image is generated.
In the techniques disclosed in these documents, a narrow field of view of an endoscope may be supplemented with a virtual endoscope image. However, the viewpoint of the virtual endoscope image is the same as that of a real endoscope image, and an observation direction of the virtual endoscope image is the same as that of the real endoscope image. Therefore, a region of interest, such as a region on which a surgery is to be performed, and a treatment tool may not be displayed in the virtual endoscope image and the real endoscope image, depending on a positional relationship among the region of interest, the treatment tool and the endoscope, and such a positional relationship may not be recognized.
Further, it is difficult to perspectively recognize an endoscope image. Therefore, in the virtual endoscope image and the real endoscope image displayed by using the techniques disclosed in these documents, it may be difficult to recognize a state in which a treatment tool becomes close to a region of interest.